Mixers are specialized modulator circuits that multiply their input signals frequency-pair by frequency-pair, often producing very complex products in the process. A typical mixer includes an input stage, which converts a voltage input to a current mode signal, and a mixer core, which essentially commutates the polarity of the current mode signal in response to a local oscillator signal, although the commutation may not be completely binary.
An important characteristic of a mixer is its small-signal linearity which defined by the 1 dB gain compression and the 3rd order intercept. The input stage of a standard mixer may include a simple differential pair of transistors. The linear range of such an input stage, however, is typically quite small which limits the attainable dynamic range. One prior art technique for extending the linear input range involves the use of multi-tanh input cells which can typically handle larger input signals without significant distortion. See, e.g., U.S. Pat. No. 5,589,791. Another prior art technique for extending the linear input range of a mixer involves the use of a class-AB as shown in U.S. Pat. No. 5,826,182.